Boosting the velocity detection limit of 3D single-cell tracking time-lapse MRI by balanced SSFP imaging.

purposeTime-lapse MRI allows for the dynamic tracking of single iron-labeled cells. However, the time required for spatial encoding creates a temporal blur and, therefore, a limited ability to resolve moving cells. To study fast moving cells, such as rolling immune cells along the endothelium during inflammatory processes, advanced accelerated acquisition techniques are required.

methodsBalanced SSFP (bSSFP) imaging is applied to phantom and in vivo murine brain time-lapse MRI measurements at 9.4 T. Its detection capability of moving iron-labeled cells is compared with conventional gradient echo imaging (GRE) for 2D Cartesian sampling and evaluated for fully sampled and accelerated reconstructions with compressed sensing for 3D interleaved radial sampling in bSSFP.

resultsBoth phantom and in vivo time-lapse MRI measurements show that single cells can be followed dynamically using bSSFP. High temporal resolution of less than 2 min reduces geometric distortion. The velocity detection limit increases to 0.8 mm/min in vitro and previously hidden fast-moving cells are recovered. Interleaved 3D radial sampling enables 3D cell tracking and simultaneous imaging at varying acceleration factors. Fivefold acceleration with compressed sensing optimizes cell visibility, image quality, and temporal resolution.

conclusionbSSFP time-lapse MRI improves single-cell tracking by enhancing temporal resolution. In vitro, the velocity detection limit is increased fourfold compared to conventional GRE. Interleaved 3D radial bSSFP offers whole-brain coverage at isotropic spatial resolution and retrospective reconstruction of both fully sampled and high temporal resolution images.